This invention relates to a separator for agricultural crops such as grain and more particularly to an improved rotor for such a machine.
Agricultural crop separators, especially those embodied in combines are well known. A combine advances over a field to gather crop material and feed it to the crop separator where typically grain is threshed out, separated from straw, chaff and other material, cleaned and delivered to a grain tank. The separator typically includes a threshing cylinder of considerable mass rotating at high speed in close proximity to an adjustable concave or grate, the radial space or clearance between the two being a threshing zone. In gathering crop material from the surface of a field, there is a risk or an unseen foreign body, such as a rock, being delivered with crop material to the threshing zone and, if the rock is significantly larger than the clearance between the concave and cylinder, serious damage may result to those parts. Further, unexpected sudden increases in the rate of feeding may occur, exceeding momentarily the capacity of the cylinder and concave and imposing excessive loads on them as well as on related drive and structural parts.
In separators of the type where a concave only partially surrounds a threshing cylinder, it is known to mount the concave in such a way that it can be deflected generally radially away from the threshing cylinder so as to pass a large foreign body. Typically, springs are used to return the concave to normal working position after the body has passed through the threshing zone. It is also known to provide the surface of the threshing bar of a conventional threshing cylinder with a flexible layer of elastomeric material, both to provide a more gentle threshing action and, it has been claimed, to provide a threshing bar which is partially deformable to provide slightly greater concave clearance for heavy flows of crop material. But the deformability of such threshing bars is very limited and certainly not sufficient to cope with potentially damaging foreign bodies and, in addition, provision for adjustment of concave to cylinder clearance must still be provided in the mounting of the concave itself in order to provide, for example, for the widely differing threshing requirements of such crops as corn and small grains. In an axial flow machine in which a cylindrical grate or concave completely surrounds a threshing cylinder, provision of a radially retractable concave or grate is less feasible. Provision for radial retraction to permit the passage of larger objects would, almost of necessity, require splitting of the cylinder. In operation, such splitting would produce discontinuities in the grate surface providing an impedance to the passage of a foreign body such as a rock and also potentially increasing mechanical damage to the grain being threshed.
In axial flow machines having a frusto-conical rotor and grate, it is known to provide for axial deflection of the rotor away from the grate when a foreign body or "slug" of material imposes sufficient force. However, unless the cone angle of the grate is quite flat, an inconveniently large axial movement is required to produce the necessary increase in clearance between rotor and grate and the support and bias structure required may become quite cumbersome.